1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and a method of manufacturing the same.
2. Description of Related Art
Recently, a liquid crystal display device adopts a structure wherein a color filter and a black matrix are formed over a thin film transistor array substrate to obtain a higher aperture ratio. The liquid crystal display device having such a structure (hereinafter, referred to simply as “the C/F and BM on array structure”) includes a top substrate, a bottom substrate, and a liquid crystal layer interposed between the two opposite substrates. The bottom substrate has an array of thin film transistors formed over the top surface of the bottom substrate, and both a black matrix and a color filter are formed over the thin film transistor array.
As described above, the liquid crystal display device having the C/F and BM on array structure has the advantage of a high aperture ratio. However, most of the liquid crystal display devices having the C/F and BM on array structure have an additional black matrix formed over the bottom surface of the top substrate in order to prevent a diffused reflection, or a reflection or dispersion of light.
FIG. 1 is a plan view illustrating arrangement of the thin film transistors and the pixels of the conventional liquid crystal display device having the C/F and BM on array substrate.
Referring to the FIG. 1, on a first substrate 10 of the liquid crystal display device, a plurality of gate lines 32 are arranged in a transverse direction and spaced apart from each other, and a plurality of data lines 36 are arranged in a longitudinal direction perpendicular to the gate lines 32 and spaced apart from each other. Pixel electrodes A1 to A9 are respectively formed over an area defined by the two adjacent gate lines 32 and two adjacent data lines 36, and thin film transistors 20 are respectively formed near cross points of the gate lines 32 and the data lines 36.
Each of the thin film transistors 20 has a gate, a source, and a drain electrode. The gate electrode, the source electrode and the drain electrode are electrically connected with the gate line 32, the data line 36, and the pixel electrode, respectively.
FIG. 2 is a cross sectional view showing the typical transmissive liquid crystal display device having the C/F and BM on array structure. Referring to FIG. 2, in the conventional liquid crystal display device, a second substrate 50 (as an upper substrate) is aligned with the first substrate 10 (as a lower substrate), a liquid crystal layer 60 is interposed between the two opposite substrates 10 and 50, and a back light device 80 is positioned under the first substrate 10.
On the first substrate 10, a gate electrode 22 of the thin film transistor 20 is formed, and a gate insulating layer 42 is formed on the exposed surface of the substrate 10 while covering the gate electrode 22.
On the gate insulating layer 42, a semiconductor island 24 of the thin film transistor 20 is formed over the gate electrode 22, and an ohmic contact layer 26 of the thin film transistor 20 is formed on the semiconductor island 24.
Further, the source and the drain electrodes 28a and 29b (spaced apart from each other) are formed covering the ohmic contact layer 26 over the semiconductor island 24, and a passivation film 48 is formed covering the thin film transistors 20, and has a contact hole 30 on a predetermined portion of the drain electrode 28b. The pixel electrode 102 is formed on the passivation film 48 and is electrically connected with the corresponding drain electrode 28b through the corresponding contact hole 30. A first black matrix 46 is formed on a portion of the passivation film 48 over the TFT.
Color filter 104 of red (R), green (G) and blue (B) are formed on the corresponding pixel electrode 102, respectively. FIG. 2 shows only the color filter layers G and R.
On the color filter 104 and the black matrix 46, a first orientation film 44 is formed and faced with liquid crystal layer 60.
On the bottom surface of the second substrate 50, a second black matrix 56 is formed. The second black matrix 56 has the almost same shape as the black matrix 46 of the first substrate 10. A common electrode 52 is formed to cover the second black matrix 56.
On the bottom surface of the common electrode 52, a second orientation film 54 is formed and faced with the liquid crystal 60.
At this point, the first black matrix 46 of the first substrate 10 serves to prevent light from passing through the gap between the gate line 32 and the pixel electrode 102 and the data line 36 and the pixel electrode 102, and shield the thin film transistors 20 from incident light. In other words, the first black matrix and the color filter are usually formed at the substrate having the thin film transistors in order to improve the aperture ratio by minimizing an alignment margin which is employed when the first and second substrates 10 and 50 are aligned with and fixed to each other.
However, the second black matrix 56 of the second substrate 50 is adopted to prevent a degradation of a contrast ratio, or a variation of the colors. The variation of colors may occur when elements of dispersed light passing through the respective color filter layers are mixed in a region of the adjacent color filter layer. It is preferred that the width of the second black matrix 56 is narrower than that of the first black matrix 46 in order not to affect the alignment margin.
Though the width of the second black matrix 56 is narrower than that of the first black matrix 46, since both the first and the second substrates have the first and second black matrices, respectively, the substrate-aligning process is complicated, leading to increase in alignment error. That is to say, the addition of the second black matrix results in an addition of an inferiority factor to the substrate-aligning process.
Further, the number of processes for forming the second black matrix 56 at the second substrate is increased due to the addition of the additional black matrices 56.
For the foregoing reason, there is a need for a liquid crystal display device that is free from the effect of the dispersion reflection, and has a high aperture ratio and a simplified substrate-aligning process.